1. Field of the Invention
The present invention relates to solar cell devices, more particularly, to a method for producing solar cell devices that scatter incident light and effectively utilize light absorbed by active layers thereof, whereby the power outputting property of the solar cell device is stably improved.
2. Related Background Art
Solar cell devices are used as energy sources in various equipments at the present time.
In solar cell devices, PN junctions or PIN junctions are used in functional portions, and silicon is generally the semiconductor which forms the PN junction. It is preferable from the viewpoint of efficiency of conversion of optical energy into electromotive force to use single crystal silicon as a semiconductor material. However, the use of amorphous silicon may be preferred for increasing the area and decreasing the cost. On the other hand, the use of polycrystalline silicon has recently been investigated to obtain solar cell devices at the low cost of amorphous silicon and the high conversion efficiency of single crystal silicon. A high efficiency of energy conversion equivalent to that of a solar cell device made of single crystal silicon has yet to be obtained.
With respect to single crystal silicon, various techniques of increasing efficiency, for example, the point-contact method (Richard M. Swanson et al., IEEE, Vol. ED-31, No. 5, MAY (1984) P661), the surface passivation technique and the technique of decreasing the electrode area (T. Nammori, Research Forum of Crystalline Solar cell devices, (1989) p77, Tokyo), the light-trapping technique (T. Uematsu et al., Conf. Record of the 20th IEEEPVSC (1988) p792) and so on, have been investigated. However, at present, all these techniques are unsatisfactory from the viewpoint of decrease in the cost since it is necessary for decreasing cost to sufficiently decrease the thickness of silicon.
In addition, conventional methods of decreasing the thickness of a single crystal silicon solar cell device can use only a plate-like substrate on which a single crystal silicon thin layer is formed by etching. The conventional methods thus have the problem that the substrate is distorted by a heat treatment process such as thermal diffusion, oxidation or the like or curved by formation of electrodes thereon. The methods also cause many difficulties in forming a microstructure, stabilizing the formation process, increasing the area and the like.
U.S. Pat. No. 4,816,420 discloses a method for producing a tandem solar cell which comprises; forming a mask layer on a crystal substrate, depositing crystalline material at exposed areas of the substrate under conditions that provide lateral growth crystalline material over the mask layer, continuing lateral overgrowth until a sheet of single crystal material is formed, separating the sheet from the substrate, forming a thin-film solar cell from the separated sheet, and bonding the solar cell to another solar cell to form a tandem solar cell.
However, it cannot be said that this method is satisfactory for providing a solar cell device comprising a relatively thin semiconductor layer having a high conversion efficiency, and there is still room for improvement. Similarly, the yield of the method also has room for improvement.